ALB vs NLB: AWS Load Balancers Compared


Here is a summary table that captures the key points covered in this article for ALB vs NLB –

Features/RequirementsApplication Load Balancer (ALB)Network Load Balancer (NLB)
Layer of OperationLayer 7 (Application Layer)Layer 4 (Transport Layer)
Traffic TypeBest for HTTP/HTTPS trafficHandles TCP, UDP, TLS traffic
Routing MechanismContent-based routing (HTTP headers, methods, paths, query parameters, source IP)Load balanced over TCP connections
PerformanceExcellent performance for HTTP/HTTPS trafficExtreme performance with ultra-low latency
ScalabilityScales automatically, suitable for varying trafficScales automatically, handles larger volume of requests
SecuritySSL/TLS decryption, integration with AWS Certificate Manager and AWS WAFPreserves client source IP, doesn’t natively support SSL/TLS offloading
IntegrationHigh integration with AWS services, native support for containerized applicationsRobust integration with AWS services
ProtocolsSupports HTTP/2 and WebSocketSupports long-lived TCP connections
PricingBased on LCUs, considering new connections, active connections, processed bytes, and Rule evaluationsBased on processed bytes and LCUs, can be more expensive for high data throughput
Ideal Use CasesComplex web applications with HTTP/HTTPS traffic, needing advanced request routingApplications with extreme performance needs, volatile traffic, and requiring a variety of protocols


As applications are increasingly deployed across multiple geographic regions, the need to distribute network traffic effectively to ensure high availability, redundancy and resiliency has become a necessity. Load Balancers are used to efficiently distribute incoming network traffic across multiple backend servers, ensuring no single server bears too much demand.

This article aims to provide a detailed comparison between two AWS (Amazon Web Services) Load Balancers: Application Load Balancer (ALB) and Network Load Balancer (NLB), to help you make an informed decision about which one is most suitable for your specific needs.

Understanding AWS Load Balancers

In the simplest terms, a Load Balancer works as a traffic cop, sitting in front of your servers and routing client requests across all servers capable of fulfilling those requests in a manner that maximizes speed and capacity utilization and ensures that no one server is overworked. AWS offers three types of Load Balancers: Classic Load Balancer (CLB), Application Load Balancer (ALB), and Network Load Balancer (NLB). This article focuses on the latter two.

Why do we need Load Balancers in Cloud Infrastructure?

Load Balancers play a critical role in maintaining the reliability and robustness of web applications and services. They’re especially important in cloud environments for a few reasons:

  • High availability and fault tolerance: Load balancers distribute traffic across multiple servers, which means if one server becomes unavailable, the load balancer redirects traffic to the remaining online servers.
  • Scalability: As traffic to your application changes over time, a load balancer can dynamically scale your resources to meet demand.
  • Efficiency: By spreading the load evenly across the server pool, load balancers ensure that no single server is overwhelmed.

AWS provides managed load balancing services that integrate with its Elastic Compute Cloud (EC2) instances. These Load Balancers are constantly updated and fine-tuned, offering compelling benefits for applications running in the AWS environment. The next sections will delve deeper into the specifics of Application Load Balancer and Network Load Balancer.

Types of Load Balancers in AWS

AWS provides three types of elastic load balancing features that cater to different application or network needs. Each one provides different capabilities and is architected to perform optimally for specific types of workloads. Below is a brief introduction to these three types:

Classic Load Balancer (CLB)

The Classic Load Balancer is the first generation of AWS load balancer. It provides basic load balancing across multiple Amazon EC2 instances and operates at both the request level and connection level. CLB is intended for applications that were built within the EC2-Classic network. Over time, AWS has developed more advanced and flexible load balancers like the ALB and NLB.

It’s important to note that Classic Load Balancer is now considered a legacy product within AWS’s suite of tools. It is crucial for developers and architects to be aware of the broader trajectory of AWS services to understand why the newer offerings (ALB and NLB) have been designed the way they are. For that reason, for the remainder of the article, our focus will be on these current offerings, which are the recommended options by AWS for most load balancing scenarios.

Application Load Balancer (ALB)

The Application Load Balancer (ALB), operating at the application layer (Layer 7), is renowned for its sophisticated routing strategies based on the request’s content. It offers significant flexibility for dealing with modern application architectures like microservices or container-based deployments and supports dynamic protocols such as HTTP/2 and WebSocket, making it highly suitable for real-time, bidirectional communication scenarios.

Related Reading: Containers on AWS

Network Load Balancer (NLB)

The Network Load Balancer (NLB) operates at the transport layer (Layer 4), and it’s designed for volatile traffic patterns handling millions of requests per second with high throughput at ultra-low latency. Ideal for applications requiring high performance like gaming, streaming, and financial applications, NLB preserves the client’s source IP and is well-equipped to handle long-lived TCP connections, beneficial for WebSocket or IoT type of applications.

Both the AWS Load balancer options – Application Load Balancer and Network Load Balancer – are equipped with robust features that can be used to cater to different application or network requirements.

Deep Dive into Application Load Balancer (ALB)

application load balancer architecture
ALB. Source: AWS Elastic Load Balancing

Understanding the intricate details of the Application Load Balancer is crucial to fully appreciate its capabilities and identify scenarios where it could be the optimal choice for your applications. This section will elaborate on its features, potential limitations, and ideal use cases.

Overview and Use Cases

As stated earlier, the Application Load Balancer operates at Layer 7 of the OSI model and can make routing decisions based on the content of the request. This advanced routing capability makes ALB an excellent choice for complex and microservices-based architectures.

ALB is ideal for HTTP and HTTPS traffic and provides advanced request routing features, including host and path-based routing, and support for containerized applications. It is suitable for applications requiring flexible management and SSL/TLS offload, real-time application traffic inspection, or WebSocket support.

ALB’s integration with ECS and EKS (Elastic Kubernetes Service) makes it an optimal choice for containerized workloads.

Benefits of Application Load Balancer

  1. Advanced Routing Capabilities: ALB can route traffic based on the content within the application traffic, allowing more granular control over load balancing.
  2. Support for Modern Protocols: ALB supports HTTP/2 and WebSocket protocols, essential for real-time, bidirectional communication.
  3. Integration with AWS Services: ALB integrates seamlessly with various AWS services like AWS WAF, AWS Auto Scaling, and Amazon CloudWatch.
  4. Support for Microservices and Containers: With its dynamic port mapping feature, ALB offers robust support for microservices and container-based applications.

Potential Limitations

While the Application Load Balancer provides several advanced capabilities, there are few potential limitations to consider:

  1. Limited Protocol Support: ALB only supports HTTP/HTTPS traffic. For non-HTTP applications or use cases requiring Layer 4 load balancing, you would need to use the Network Load Balancer or Classic Load Balancer.
  2. UDP Traffic: ALB does not support the UDP protocol. If your application uses UDP, you’d need to use the Network Load Balancer or a third-party solution.
  3. Cost: Depending on the size and scale of your application, the cost could potentially be higher compared to the Network Load Balancer as pricing is based on LCU (Load Balancer Capacity Units) usage which considers processed bytes, new connections, and active connections.

When to Use Application Load Balancer

  • Consider using ALB in scenarios where you need advanced routing features, such as path or host-based routing, or where you need tight integration with other AWS services.
  • ALB is also an excellent choice for applications built around microservices or those that utilize container-based architectures.
  • ALB is very well-suited for applications requiring real-time, bidirectional communication, given its native support for protocols like HTTP/2 and WebSockets.
  • ALB is beneficial in cases where you need to inspect application traffic in real-time for making intelligent routing decisions.

Related Reading: Top Cloud Architecture Interview Questions

Deep Dive into Network Load Balancer

The Network Load Balancer is an excellent choice for load balancing TCP, UDP, and TLS traffic where extreme performance is required. To understand when and why to use NLB, let’s dive into its features, potential limitations, and ideal use cases.

network load balancer architecture
NLB. Source: AWS Elastic Load Balancing

Overview and Use Cases

The Network Load Balancer is built to handle tens of millions of requests per second while maintaining high throughput at ultra-low latencies. It operates at Layer 4 of the OSI model and is ideal for applications that require extreme performance and low latencies.

NLB excels at handling sudden and volatile traffic patterns. It is also capable of maintaining long-lived connections, which makes it perfect for WebSocket or IoT applications.

Furthermore, Network Load Balancer is the only AWS load balancer that supports the handling of TCP, UDP, and TLS traffic together. If your application runs on these protocols, NLB might be the optimal choice.

Benefits of Network Load Balancer

  1. Extreme Performance and Scale: NLB is designed to handle volatile traffic with millions of requests per second and maintains high throughput at ultra-low latency.
  2. Preserving Source IP: Unlike other load balancers, NLB can preserve the source IP of the clients, allowing applications to process requests using the client’s IP address.
  3. Long-Lived TCP Connections: NLB is built to handle long-lived TCP connections, which is ideal for real-time applications like gaming, streaming, messaging, and IoT.
  4. Support for Multiple Protocols: Unlike ALB, NLB supports TCP, UDP, and TLS protocols, providing the flexibility to handle a wide range of applications.

Potential Limitations

Just like any other service, NLB has its own set of potential limitations:

  1. Content-Based Routing: Unlike ALB, NLB cannot make routing decisions based on the content of the request. If your application needs content-based routing, Application Load Balancer is a better choice.
  2. HTTP Specific Features: NLB lacks HTTP-specific features available in ALB like host-based routing, path-based routing, or HTTP headers-based routing.
  3. Integration with AWS Services: As of my knowledge cutoff in September 2021, NLB lacks the same level of integration with some AWS services that ALB offers. For instance, NLB doesn’t integrate natively with AWS WAF or AWS Shield.
  4. No Native SSL/TLS Offloading: NLB does not natively support SSL/TLS offloading, which might increase the computational load on your servers if your applications require these protocols.

When to Use Network Load Balancer

Consider using the Network Load Balancer in the following scenarios:

  • When you need to handle a volatile amount of network traffic, especially for TCP, UDP, or TLS protocols.
  • When maintaining a high number of persistent connections with ultra-low latency is a requirement.
  • When applications need to preserve the source IP for client identification or security purposes. (Related Reading: IDS/IPS on AWS)
  • If your use case involves extreme performance requirements, such as in gaming or real-time streaming applications.
  • For applications where the lack of HTTP-specific features, such as host-based or path-based routing, is not a limiting factor.
  • When end-to-end encryption (no SSL/TLS offloading) is necessary or desired for your application’s traffic.

Application Load Balancer vs Network Load Balancer: Head-to-Head Comparison

Making the right choice between ALB and NLB can be easier with a side-by-side comparison. Let’s explore the key differences between these two types of AWS load balancers.

1. Performance

ALB: It offers robust performance for HTTP and HTTPS traffic, with support for HTTP/2 and WebSocket for even more efficient communication.

NLB: Designed for extreme performance, it can handle tens of millions of requests per second and offers ultra-low latencies, making it ideal for handling sudden and volatile traffic patterns.

2. Scalability

ALB: It scales automatically and is capable of handling sudden increases in traffic, ideal for web applications with varying traffic patterns.

NLB: It also scales automatically but is more suitable for extreme traffic conditions, given its design to handle a larger volume of requests per second.

3. Security

ALB: It offers SSL/TLS decryption and allows for integration with AWS Certificate Manager for easy SSL/TLS certificate deployment. ALB can also be integrated with AWS WAF, enhancing the application’s security.

NLB: It preserves the client’s source IP address, which could be beneficial for applications that require client IP for processing. However, NLB does not natively support SSL/TLS offloading.

4. Flexibility and Versatility

ALB: With its advanced request routing based on the content of the request, ALB offers more flexibility for complex web applications. It also integrates better with container-based applications and microservices architecture.

NLB: It offers flexibility in terms of handling different protocols (TCP, UDP, TLS), making it versatile for non-HTTP applications. It also supports long-lived TCP connections, which can be crucial for certain application types.

5. Pricing

ALB: Pricing is based on Load Balancer Capacity Units (LCUs), which depend on the number of new connections, active connections, processed bytes, and Rule evaluations.

NLB: Pricing depends on the number of processed bytes and the number of Load Balancer Capacity Units (LCUs), making it potentially more expensive for applications with high data throughput.

6. Use Cases

ALB: Ideal for complex web applications with HTTP/HTTPS traffic, needing path-based or host-based routing, and applications that require integration with other AWS services.

NLB: More suitable for applications needing to handle a variety of protocols, extreme performance, low latency, sudden traffic spikes, and long-lived TCP connections.

Remember, the decision should not be based solely on a feature-by-feature comparison but should also consider your specific application requirements, anticipated traffic patterns, and necessary integrations.


In conclusion, both the Application Load Balancer (ALB) and the Network Load Balancer (NLB) offer unique benefits and are suitable for different use cases. ALB shines when handling HTTP/HTTPS traffic and in complex web application scenarios that require advanced request routing. On the other hand, NLB is ideal for applications requiring extreme performance, low latency, and the handling of various protocols.

The choice between ALB and NLB should be guided by the specific requirements of your application, expected traffic patterns, and desired integration with other AWS services. The objective is to choose a load balancer that best supports your application’s performance and scalability while ensuring cost-effectiveness.

We hope this article has provided you with a solid understanding of the differences between ALB and NLB and will assist you in making an informed decision for your AWS load balancing needs.

Frequently Asked Questions

1. What are the key differences between Application Load Balancer (ALB) and Network Load Balancer (NLB)?

ALB operates at the application layer (Layer 7), handling HTTP/HTTPS traffic and offering advanced request routing based on content. NLB operates at the transport layer (Layer 4), handling TCP, UDP, and TLS traffic, and is designed for extreme performance and low latency.

2. When should I use an Application Load Balancer?

Use ALB when dealing with HTTP/HTTPS traffic, when you need advanced routing rules based on the request content, or when your applications require integration with other AWS services like AWS WAF, Amazon CloudWatch, and AWS Auto Scaling.

3. When should I use a Network Load Balancer?

Use NLB when your application needs to handle a variety of protocols, requires extreme performance and low latency, experiences sudden traffic spikes, or requires long-lived TCP connections.

4. Can I use both Application Load Balancer and Network Load Balancer for the same application?

Yes, it is possible to use both for the same application, depending on your application’s needs. However, such a setup might be complex and unnecessary for most applications.

5. Are there any limitations to using Application Load Balancer and Network Load Balancer?

Yes, ALB does not support non-HTTP/HTTPS protocols, and NLB doesn’t natively support SSL/TLS offloading. Also, the pricing models are based on LCUs and processed bytes, which can be more expensive for high data throughput applications in the case of NLB.